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Internet Draft R. Monsour, Hi/fn, Inc.
Expires in six months R. Pereira, TimeStep Corporation
A. Shacham, Cisco Systems
July 30, 1997
IP Payload Compression Protocol Architecture
<draft-ietf-ippcp-arch-00.txt>
Status of this Memo
This document is an Internet-Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet-Drafts draft documents are valid for a maximum of six months
and may be updated, replaced, or obsolete by other documents at any
time. It is inappropriate to use Internet-Drafts as reference =
material
or to cite them other than as "work in progress."
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
Distribution of this memo is unlimited.
Abstract
This memo describes an architecture for applying lossless compression
to Internet Protocol datagrams. It defines several of the key
architectural elements of a compression protocol and describes
alternatives for each element.
Acknowledgments
The authors gratefully acknowledge the many sources of input who made
this draft possible, including Rodney Thayer, Bob Moskowitz, Naganand
Doraswamy, Thomas Narten and all those that participated in the early
discussions and debates of these concepts. It is hoped that the
continued focused effort of those involved in the IPCCP Working Group
will result in the rapid development of a useful IP compression
protocol.
R. Monsour, R. Pereira, A. Shacham [Page =
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Internet Draft draft-ietf-ippcp-arch-00.txt July 29, =
1997
Table of Contents
1. Introduction...................................................2
1.1. Background................................................2
1.2. IP Payload Compression Overview...........................3
1.3. Specification of Requirements.............................3
2. Use of IP Compression with IPSec...............................3
2.1. General Compression Processing............................3
2.2. Alternative Compression Protocol Approaches...............4
2.2.1. The IP Encapsulation Approach........................4
2.2.2. The IP Header Approach...............................5
2.2.3. Comparison of the Two Approaches.....................7
2.3. Interaction of IP Payload Compression with AH & ESP.......7
3. IP payload Compression without IPSec...........................7
4. Anti-expansion of Payload Data.................................8
5. Stateless vs. Stateful compression.............................8
6. Negotiation Mechanisms for IP Compression......................8
6.1. Use of ISAKMP in IPSec Contexts...........................9
6.1.1. Compression as a "Protocol"..........................9
6.1.2. Compression as a Protocol Attribute.................10
6.2. Static Configuration for Non-IPSec Contexts..............10
7. Implications with Ipv4 and Ipv6...............................11
8. Compression Method/Format Registration Mechanism..............11
9. Document Roadmap..............................................11
10. Security Considerations......................................12
11. References...................................................13
12. Authors' Addresses...........................................14
13. Working Group................................................14
1. Introduction
This document is a submission to the IETF IP Payload Compression
Protocol (IPCCP) Working Group. Comments are solicited and should be
addressed to the working group mailing list =
(ippcp@external.cisco.com)
or to the editor.
1.1. Background
The motivation for the development of the IP Payload Compression
Protocol was initially driven by the use of the IP Security protocol
and the negative effect that IP encryption has on data link layer
compression techniques. Encrypted data is random in nature and not
compressible. When an IP datagram is encrypted, compression methods
used at lower protocol layers, e.g., the PPP Compression Control
Protocol [RFC-1962], are rendered ineffective. If both compression
and encryption are desired, compression must be performed first. Such
R. Monsour, R. Pereira, A. Shacham [Page =
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Internet Draft draft-ietf-ippcp-arch-00.txt July 29, =
1997
motivation drove the creation of a new working group, the IP Payload
Compression Protocol working group, and the development of this
document.
1.2. IP Payload Compression Overview
The IP payload compression architecture is designed to provide
compression services for the IP Protocol. Two fundamental =
requirements
of such a compression protocol are: (1) that it supports the use of
any lossless compression method, and (2) the two communicating =
parties
have a mechanism to negotiate the use of specific compression method
and any related parameters.
This document describes the architectural alternatives available for
supporting lossless compression services for IP datagrams. The
following topics are discussed:
a) alternative approaches for integrating compression with IP
Security
b) features of an IP compression protocol
c) negotiation and use of lossless compression techniques, both in
the presence and absence of the IP Security protocol
d) requirements for a registration mechanism used for identifying
compression methods for use with the protocol
e) a document roadmap to simplify access and understanding of the
necessary specifications
1.3. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC-2119].
2. Use of IP Compression with IPSec
2.1. General Compression Processing
The compression processing of IP datagrams has two phases, =
compressing
of outbound IP datagrams and decompressing of inbound datagrams.
The compression of outbound IP datagrams MUST be done before any IP
security processing, such as encryption and authentication, and =
before
any fragmentation of the IP datagram. Similarly, the decompression =
of
inbound IP datagrams MUST be done after the reassembly of the IP
datagrams, and after the completion of all IP security processing,
such as authentication and decryption. Processing of inbound IP
R. Monsour, R. Pereira, A. Shacham [Page =
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Internet Draft draft-ietf-ippcp-arch-00.txt July 29, =
1997
datagrams MUST support both compressed and non-compressed IP
datagrams.
A different compression algorithm may be negotiated in each direction
of the communication channel, or only one direction may be =
compressed.
2.2. Alternative Compression Protocol Approaches
Two recent Internet Drafts have been submitted by members of the
working group, each offering a different approach to the application
of lossless compression to IP datagram payloads. Note that in the
description of both approaches, examples are provided in the more
complex IP Security context. The simplification of the resulting
packet formats for non-IPSec environments should be apparent from the
examples.
2.2.1.T
he IP Encapsulation Approach
The first approach, what we=92ll call IP encapsulation, is described =
in
[Shacham]. This approach involves the following steps (Note: this is =
a
simplified view of the processing):
a) a complete IP datagram is treated as a payload and is compressed
b) a new IP header is prepended to the datagram to be compressed
c) subsequent IP security processing, if any, is applied to the new
datagram
The following is an example datagram structure which results when
using this approach in conjunction with ESP. This approach can be =
used
with AH as well as without any security processing of the datagram.
R. Monsour, R. Pereira, A. Shacham [Page =
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